Griff E R
Department of Biological Sciences, University of Cincinnati, Ohio 45221-0006.
Invest Ophthalmol Vis Sci. 1990 Nov;31(11):2353-60.
Electrophysiologic responses were recorded in vitro from the retina of the toad, Bufo marinus. In the isolated retinal pigment epithelium (RPE)-choroid preparation, a decrease in the K+ concentration outside the apical membrane evoked a sequence of trans-epithelial (TEP) and membrane potential changes. A hyperpolarization originating at the RPE apical membrane that increased the TEP was followed by a delayed hyperpolarization originating at the basal membrane that decreased the TEP. This response sequence differed from the well-studied bullfrog RPE in exhibiting potentials generated at the basal membrane; it more closely resembled responses from the reptilian and avian RPE. The toad direct-current electroretinogram recorded from a neural retina-RPE-choroid preparation also differed from other amphibians and was more similar to responses recorded in reptiles, birds, and mammals. In this initial study, the electrophysiologic characteristics of the RPE's Na+/K+ pump were examined. Contrary to a previous report, ouabain, a specific inhibitor of the pump, depolarized the apical membrane and decreased the TEP. Ba2+ was used to block apical K+ conductance and unmasked a modulation of the Na+/K+ pump by subretinal K+. Decreasing the K+ concentration in the presence of Ba2+ depolarized the apical membrane and decreased the TEP. These responses were blocked by ouabain, indicating that the K+ concentration decrease slowed the Na+/K+ pump.
在体外记录了海蟾蜍（Bufo marinus）视网膜的电生理反应。在分离的视网膜色素上皮（RPE）-脉络膜标本中，顶端膜外K⁺浓度降低引发了一系列跨上皮电位（TEP）和膜电位变化。始于RPE顶端膜并使TEP增加的超极化之后，是始于基底膜并使TEP降低的延迟超极化。该反应序列与经过充分研究的牛蛙RPE不同，表现为在基底膜产生电位；它更类似于爬行动物和鸟类RPE的反应。从神经视网膜-RPE-脉络膜标本记录的蟾蜍直流视网膜电图也与其他两栖动物不同，更类似于在爬行动物、鸟类和哺乳动物中记录的反应。在这项初步研究中，研究了RPE的Na⁺/K⁺泵的电生理特性。与之前的报告相反，该泵的特异性抑制剂哇巴因使顶端膜去极化并降低了TEP。Ba²⁺用于阻断顶端K⁺电导，并揭示了视网膜下K⁺对Na⁺/K⁺泵的调节作用。在Ba²⁺存在的情况下降低K⁺浓度会使顶端膜去极化并降低TEP。这些反应被哇巴因阻断，表明K⁺浓度降低使Na⁺/K⁺泵减慢。
